Refrigeration systems are commonly used in supermarkets to refrigerate or to maintain in frozen state perishable products, such as foodstuff.
Conventionally, refrigeration systems include a network of refrigeration compressors and evaporators. Refrigeration compressors mechanically compress refrigerant vapor, which is circulated from the evaporators, to increase its temperature and pressure. The resulting high-temperature refrigerant vapor, under high-pressure, is circulated to a refrigerant condensing means where the latent heat from the vapors is absorbed. As a result, the refrigerant vapor liquefies into refrigerant liquid. The refrigerant liquid is circulated through refrigerant expansion valves, thereby reducing the temperature and pressure, to the evaporators wherein the refrigerant liquid evaporates by absorbing heat from the surrounding foodstuff.
In colder environments having temperatures similar to those found in, for example, the northern part of the United States or Canada during colder periods of the year, such as winter, the condensing pressure and temperature of the refrigerant in the refrigerant condenser means are subject of the surrounding ambient air temperature. Thus, the surrounding ambient air may serve to cool the refrigerant vapor, reducing the condensing pressure required from the compressors for condensing the refrigerant vapor. Indeed, it has been estimated that energy requirements for a given refrigeration capacity may be reduced on average by 30% in such colder environments or during such colder periods. Thus, it is entirely conceivable that, in such colder periods or environments, some compressors in a refrigeration system may be unused or operate at lower energy requirements, thus conserving energy.
However, low condensing pressure has negative impacts on some aspects of a typical refrigeration system. For example, low condensing pressure may result in refrigerant liquid having insufficient pressure to properly feed the refrigerant expansion valves. Further, in typical refrigeration systems, heat is given off, or rejected, by the refrigerant condensing means as the refrigerant vapor is cooled in the refrigerant condensing means. This heat is rejected latent heat from the refrigerant, generated by the system, which, unless reclaimed, becomes lost latent heat which, in turn, constitutes wasted energy, especially when the refrigerant condensing means is located outside, such as is typically the case for air-cooled refrigerant condenser means. This lost latent heat is particularly disadvantageous during colder periods or in colder environments, i.e. where lower condensing pressure may be used to reduce energy requirements for compressors, as it is desirable in such environments to conserve the latent heat for purposes of, among other things, comfort heating of a building in which the refrigeration system is located. It is possible to reduce the wasted energy by installing a heat reclaim means to reclaim the rejected latent heat, as it is given off by the condenser, thus reducing loss of the latent heat. However, low condensing pressure can result in low condensing temperature of refrigerant vapor. In such circumstances, latent heat released upon heat reclaim will be at the low condensing temperature, which may be insufficient for use of the heat for any useful purpose.
In addition, low condensation pressure generated in compressors may also have negative impacts on system defrost capabilities. For example, many refrigeration systems use the so-called hot refrigerant gas defrost method wherein hot refrigerant gas is re-routed backward from the compressors, where it is converted to refrigerant liquid, thereby giving off heat that defrosts the evaporator. However, low condensing pressure may result in the refrigerant being insufficiently pressurized to circulate thereafter to either the condenser means or the evaporators for subsequent usage thereby.
Accordingly, it would be advantageous to have a refrigeration system that allows for use of lower condensing pressure while providing sufficient heat reclaim of rejected latent heat for useful purposes, such as comfort heating, and maintaining efficient defrost cycles.